1. Field of the Invention
This invention relates to a lens assembly, and more particularly to a lens assembly provided with an automatic focusing device for moving a focusing lens system to an in-focus position.
2. Description of the Prior Art
When an automatic focusing device is incorporated into an interchangeable lens assembly so that the distance of an object can be detected solely within the lens assembly and the focusing lens in the lens assembly can be moved to an in-focus position, automatic focusing photography becomes possible even when the lens assembly is mounted on a camera body without an automatic focusing device incorporated therein. However, the interchangeable lens assembly of an interchangeable lens type camera generally has a large diameter and is heavy. Accordingly, incorporation of an automatic focusing device therein would result in a further increase in the diameter and weight of the interchangeable lens assembly which in turn would make handling the camera more difficult.
Various constructions for providing an automatic focusing device on the barrel of an interchangeable lens assembly have heretofore been proposed and these constructions may be roughly grouped into two general types. The first type includes a distance detecting module, a battery and a focus driving system arranged as a unit on the lower portion of the lens barrel. This construction, which necessarily results in a downwardly bulging configuration of the lens assembly when mounted onto a camera body, has led to the following disadvantages:
1. During photography with the camera hand held, the operator's finger is liable to cover the distance detecting window so that an incorrect distance detection sometimes occurs; PA1 2. During photography with the camera mounted on a tripod, the bulge on the lower portion of the lens barrel becomes a hindrance and good operability is not obtainable; PA1 3. The downwardly bulging lens configuration fails to provide a compact camera design; and PA1 4. If a portion of a drive unit or the like for the camera juts out, the bulge on the lower portion of the lens assembly may strike against such portion when the lens assembly is mounted on the camera body, thus preventing good handling or easy mounting. PA1 The second type includes a distance detecting module, a battery and a focus driving system arranged as a unit on the upper portion of the lens barrel. This construction results in an upwardly bulging configuration of the lens assembly when mounted to a camera body and has led to the following disadvantages: PA1 5. When a strobe unit is disposed above the pentaprism of the camera body, the light adjusting window of the strobe is hidden; PA1 6. When use is made of a camera of the type in which the aperture value or the like is read through the viewfinder, the vicinity of the aperture value becomes so dark that the aperture value is difficult to read; PA1 7. The upwardly bulging lens configuration fails to provide a compact camera design; and PA1 8. If a portion of a motor drive unit or the like for the camera juts out, the bulge on the upper portion of the lens assembly may strike against such portion when the lens assembly is mounted on the camera, thus preventing good handling or easy mounting.